In some vehicles vacuum is used to operate or assist in the operation of various devices. For example, vacuum may be used to assist a driver applying vehicle brakes, turbocharger operation, fuel vapor purging, heating and ventilation system actuation, and driveline component actuation. If the vehicle does not produce vacuum naturally, such as from the intake manifold, then a separate vacuum source is required to operate such devices. For example, in some boosted engines where intake manifold pressures are often at pressures greater than atmospheric pressure, intake manifold vacuum may be replaced or augmented with vacuum from an evacuator.
As used herein, an evacuator is defined as a converging, diverging nozzle assembly with three connections, a motive port connected to the intake air at atmospheric pressure, a discharge port connected to the manifold vacuum located downstream of the throttle, and a suction port connected to a device requiring vacuum. A low pressure region may be created within the evacuator so that air can be drawn from a vacuum reservoir or may directly act on a device requiring vacuum, thereby reducing pressure within the vacuum reservoir or device requiring vacuum. In general, there is a continuing need in the art for improved evacuators that generate increased vacuum pressure and increased suction mass flow rate while decreasing the consumption of engine air.
A control valve may be used to shut off or stop compressed air from flowing through the evacuator if the engine is operating under boosted pressures. Specifically, the control valve is used to prevent compressed air located at the intake manifold from flowing through the evacuator, and back into the intake air, which is at atmospheric pressure. However, several drawbacks exist when using this approach. For example, the evacuator may only be able to provide vacuum if the engine is not operating under boosted pressures, since the control valve shuts off the flow of compressed air when the engine operates under boosted pressures. Moreover, the control valve is typically an expensive component that adds significantly to the overall cost of the system. Thus, there is a continuing need in the art for an improved, cost-effective evacuator for use in a boosted engine that may eliminate the need for a control valve.
Finally, it should also be appreciated that the evacuator may be defined by a housing assembly. The housing assembly includes a body and one or more suction caps. The suction caps are used to connect the body of the housing to a vacuum canister. Sometimes a check valve may be positioned within the housing of the ejector or the aspirator, between the body and the suction cap. The check valve may ensure that air does not pass from the evacuator, which may be an aspirator or an evacuator, to the vacuum canister.
The body and the suction caps may be welded or otherwise joined to one another to create the housing assembly. However, in order to assure that the housing assembly is substantially fluid-tight and does not allow for air to enter the interior of the housing, the weld joint between the body and the suction cap should not only be mechanically rigid, but also provide a fluid-tight seal. In other words, the weld between the body and the suction cap needs to provide a pneumatic seal to substantially prevent the ingression of air or other fluids into the housing assembly. This requirement may be challenging to meet, and requires relatively stringent inspection requirements which may add to the overall assembly and manufacturing cost of the part. Thus, there is a continuing need in the art for cost-effective ejectors and aspirators that still meet air leakage requirements.